1. Field of Invention
The present invention relates to a semiconductor transport device. More particularly, the present invention relates to a vacuum suction membrane for holding a silicon wafer.
2. Description of Related Art
Wafer transport systems use a variety of mechanisms for transport, the most common and widely used method of which is creating a vacuum to suck up a silicon wafer. The vacuum suction method is used, for example, in a chemical-mechanical polishing device to hold a silicon wafer.
FIG. 1 is simplified and localized cross-sectional view of a conventional chemical-mechanical polishing device. As shown in FIG. 1, the chemical-mechanical polishing device includes a polishing head 100 and a polishing table 110. A polishing pad 120 covers the polishing table 110. The polishing head 100 further includes a gripping pan 102 having an elastic membrane 106 therein. When the polishing head 100 presses upon a silicon wafer 108, the downward pressure produced by the polishing head 100 on the wafer 108 is evenly spread out so that the wafer 108 can be polished smoothly.
However, at the end of a chemical-mechanical polishing operation, an external robotic arm is often used to unload the wafer 108 from the polishing table 110 and then transfer the wafer 108 elsewhere. To smooth the process and reduce operating cost, the polishing head 100 often incorporates a vacuum system. In other words, the gripping pan 102 structure is frequently modified to include a set of internal gaseous pipelines. In addition, a multiple-hole panel is inserted between the gripping pan 102 and the membrane 106 such that the membrane 106 also encloses the bottom section of the multiple-hole panel. After a chemical-mechanical polishing operation, a vacuum system may be triggered to create a vacuum state inside the polishing head 100 through the set of internal gaseous pipelines. Hence, the membrane 106 originally pressed against the wafer 108 now attaches to the wafer 108 through suction. Thereafter, the polishing head 100 may move to carry the wafer 108 away. On releasing the vacuum inside the polishing head 100, suction between the membrane 106 and the wafer 108 disappears and the wafer 108 drops off from the polishing head 100.
FIG. 2 is a schematic top view of a conventional multiple-hole panel inside a vacuum-suction polishing head. As shown in FIG. 2, the multiple-hole panel 200 has a shape that corresponds to a silicon wafer. Hence, the multiple-hole panel 200 is circular and contains a number of holes 202. At the end of a polishing operation, the polishing head is turned into a vacuum state. Through differential pressure acting via the holes 202, the elastic membrane 106 contracts into the hole 202 resulting in a suction pressure on the wafer.
However, the conventional technique has some drawbacks in real applications. The polishing head must return to normal pressure after a polishing operation so that the wafer attached to the membrane can drop off. Due to considerable suction between the membrane and the wafer, the wafer may not unload normally. In other words, the wafer is still attached to the membrane after the polishing head has returned to a normal pressure. Eventually, the wafer may be damaged due to subsequent mishandling.
In addition, because there is no membrane between the multiple-hole panel for sucking up the wafer and the wafer, the process of creating a suction vacuum also carries some micro-particles from the surrounding atmosphere towards the wafer leading to wafer contamination.